Some devices(nbd) can becomes unoperatable via kill_bdev
so its pagecache will be invalidated and all buffers becomes unmapped.
In that situation we will trigger BUGON on submit_bh.
#Testcase
mkdir -p a/mnt
cd a
truncate -s 1G img
mkfs.ext4 -F img
qemu-nbd -c /dev/nbd0 img
mount /dev/nbd0 /mnt
cp -r /bin/ /mnt&
# Disconnect nbd while cp is active
qemu-nbd -d /dev/nbd0
Signed-off-by: Dmitry Monakhov <dmonakhov@xxxxxxxxxx>
---
fs/jbd2/journal.c | 12 ++++++++++++
1 file changed, 12 insertions(+)
diff --git a/fs/jbd2/journal.c b/fs/jbd2/journal.c
index 81e6226..f2760c8 100644
--- a/fs/jbd2/journal.c
+++ b/fs/jbd2/journal.c
@@ -1333,6 +1333,18 @@ static int jbd2_write_superblock(journal_t *journal, int write_op)
if (!(journal->j_flags & JBD2_BARRIER))
write_op &= ~(REQ_FUA | REQ_FLUSH);
lock_buffer(bh);
+ /*
+ * Some disk drives may invalidate its page cache on failure
+ * so sbh becomes unmapped.
+ */
+ if (!buffer_mapped(bh)) {
+ /* Disk dissapeared under us, there is nothing we can
+ do but complain */
+ printk(KERN_ERR "JBD2: journal superblock was invalidated "
+ "for %s.\n", journal->j_devname);
+ return -EIO;
+ }
+
if (buffer_write_io_error(bh)) {
/*
* Oh, dear. A previous attempt to write the journal
--
1.8.3.1
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